It is recognized in the prior art that at times it is desirable, if not essential, to maintain a closure such as a door in a closed condition. For example, when an automobile is involved in an accident it is a common belief that it is best if the doors remain closed to prevent the occupants from being thrown from the automobile onto the roadway or roadside. It has been found, however, that in an accident where the automobile is subjected to substantial force that the doors of the automobile will swing open under the impact of the collision due to distortion of the door frame permitting the door latch to disengage from the door strike. Similarly, emergency or fire doors which preferably are to remain locked during a fire oftentimes spring open due to distortion of the door or door frame member, permitting the door latch to disengage from the door strike. Similarly, distortion and disengagement of door members can occur when excessive force is applied to a door member such as a result of the force of water being applied from a fire hose during a fire.
In the prior art, various attempts have been made to provide exit devices which preclude the accidental opening of a closure such as a door by distortion of a door member. U.S. Pat. No. 2,709,612 is directed to an exit device for use on an automobile door to prevent accidental opening of the door by distortion of the car frame. The disclosed device includes provisions for a door member which projects beyond a free or unhinged edge of the door and cooperating socket means in a doorjamb for reception of the door member when the door is closed. In order to provide the desired interlocking engagement, the outer free or projecting end of the door member is offset from its root portion in a direction vertically and/or inwardly with respect to the cooperating doorjamb to provide an overhang and the socket means is correspondingly formed in the jamb to receive the offset door member. In one preferred form, the closure device includes a lug or dovetail member secured to a free end of the door so as to project outwardly beyond and away from such edge a short distance, this member being adapted and arranged for reception in a cooperating socket member in the frame. Preferably the lug and its cooperating socket are placed as close to the door latch member as is conveniently possible to affect maximum resistance to edgewise separation at that point. U.S. Pat. No. 4,401,330 discloses a locking method of and means for securing or maintaining secured a closure such as a door when the door members are subjected to thermal distortion caused by a fire. It is stated that the opening or disengagement of the door latching device is caused because the door frame member such as a mullion which retains the door strike is fixed at its lower end to the floor and at the upper end to the ceiling. Upon heating the door member attempts to become elongated. However, because of being fixed the door member cannot expand, causing distortion and deformation and subsequent disengagement of the locking or latching device. To avoid this distortion and disengagement, the '330 patent suggests having a free space at either the top or bottom of the frame member so as to permit elongation without distortion. According to the disclosure of the patent a latch mechanism is provided which under normal conditions is always in disengagement but upon elongation due to thermal forces will become engaged and retain the door and door frame such as a mullion in locking relation. U.S. Pat. No. 4,437,693 discloses a latching mechanism which upon the presence of excessive heat as on the occurrence of fire has a cover which melts, allowing a blocking plate to slide into operative position to prevent retraction of the latching means and consequently preventing unlatching of the device. The patent provides for a kit member to enable the utilization of the blocking member in an existing door frame.
Although the aforesaid patents define the problem confronting the present applicant, the solutions to the problem are not completely acceptable because of complexity and/or the need for modifying the closure structure.